The present invention relates to the field of motor vehicle transmissions.
It relates to the control of the claw coupling of a gearbox during gear changes requiring the mastery of the speed differential between the gearbox elements to be claw-coupled, in the absence of a friction mechanical synchronization system.
The object of this invention is a method for controlling the claw coupling of a vehicle gearbox.
It is preferably used on, but not limited to, a hybrid transmission for a motor vehicle provided with a heat engine and a drive electric machine including two concentric primary shafts each bearing at least one reduction gear on a secondary shaft connected to the vehicle wheels, such as described in the publication WO2012/131259.
This transmission, illustrated by FIG. 1, includes a solid primary shaft 1 connected directly by means of a filtration system (damper hub, “damper”, double flywheel or other element) 2, to the inertia flywheel 3 of a heat engine (not shown). The solid shaft 1 bears an idler gear 4 which can be connected therewith by a first coupling system 5 (claw, synchronizer, or other type of optionally progressive coupler). A hollow primary shaft 6 is connected to the rotor of an electric machine 7.
The hollow shaft 6 bears two fixed gears 8, 9. It can be connected to the solid primary shaft 1 by means of the coupling system 5, with or without a mechanical synchronizer. A secondary shaft 10 bears two idler gears 11 and 12. The idler gears 11, 12 can be connected to the primary shaft by means of a second coupling system 13, with or without a mechanical synchronizer. The secondary shaft 10 also bears a fixed gear 14 and a reduction gear 15 toward a differential connected with the wheels (not shown) of the vehicle.
The first coupling means 5 can occupy at least three positions, wherein:                the heat engine is decoupled from the drive train connecting the electric machine 7 to the wheels,        the heat engine drives the wheels with or without the assistance of the electric machine, and        the heat engine and the electric machine 7 are coupled such as to add up the respective torques thereof in the direction of the wheels.        
The second coupling means 13 also has three positions, wherein it is in a neutral position, or either one of the two idler gears 11, 12 are claw-coupled on the secondary shaft 10.
When no mechanical synchronization means is provided on the coupling systems 5 and 13, the passage from one kinematic mode to the other requires the electronic control of the synchronization of the elements to be claw-coupled. The design of the teeth located on the coupling systems 5 and 13 can require mastery of a certain speed differential between the elements to be claw-coupled, in order to provide the coupling. It is the task then of a computer to control this speed differential.
The teeth of the elements to be claw-coupled can have various shapes. When they are straight (rectangular) as in FIG. 2A, or with “anti-releases”, as in FIG. 2B, the tooth-to-tooth contact surface is considerable. If the two parts are exactly at the same speed, there is a risk of tooth-to-tooth abutment, and therefore of unsuccessful claw coupling. It is then necessary to keep a certain difference in speed between the elements to be claw-coupled, such that they find relative positions allowing claw coupling.
Once this speed differential has been established, the order for claw coupling (or for coupling) can be given, in order to translate the coupling system.
The technical problem to be solved in order to perfect the coupling operation is then the following: maintaining the speed differential up to the claw coupling moment, at the risk of failure, while at the very instant of the claw coupling, the mechanics cause synchronism of the coupled parts (i.e. a zero speed differential).